1. Field of the Invention
The present invention relates to a wireless communications. More particularly, the present invention relates to adaptive calibration of a receiver system.
2. Description of the Related Art
With the advent and proliferation of digital communications systems, the need for low cost, high performance radio receivers continues to accelerate. These needs have prompted a strong interest in the development of direct conversion receiver architectures that implement a single conversion from a wireless link carrier frequency to a baseband frequency. The reduced complexity of direct conversion receivers holds great potential for reduced cost and increased performance.
Many modern digital communications systems use a form of quadrature modulation in which the wireless signal includes in-phase (I) and quadrature (Q) components which carry information with a relative phase offset of 90°. Typically, the in-phase and quadrature components are received using two distinct signal paths within a direct conversation receiver. Any difference in the gain or phase between the two paths corrupts the information in the signal. In addition, any DC offset or low frequency noise voltage which is generated by the receiver also corrupts the information in the signal.
In order to reduce the corruption, direct conversion receivers often employ an adaptive calibration mechanism. For example, prior art systems have been proposed which include a non-coherent adaptive calibration mechanism. However, such non-coherent adaptive calibration mechanisms exhibit high noise figures and, thus, do not accurately calibrate for receiver imperfections.
Therefore, there is a need in the art to develop an adaptive calibration system which provides accurate, low noise calibration.